1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device implementing in-plane switching (IPS) where an electric field to be applied to liquid crystal is generated in a plane parallel to a substrate.
2. Discussion of Related Art
A liquid crystal display (LCD) device uses the optical anisotropy and polarization properties of liquid crystal molecules to produce images. Liquid crystal molecules have a definite orientational alignment as a result of their long, thin shapes. That orientational alignment can be controlled by an applied electric field. In other words, as an applied electric field changes, so does the alignment of the liquid crystal molecules. Due to the optical anisotropy, the refraction of incident light depends on the orientational alignment of the liquid crystal molecules. Thus, by properly controlling an applied electric field, a desired light image can be produced.
While various types of liquid crystal display devices are known, active matrix LCDs having thin film transistors and pixel electrodes arranged in a matrix are probably the most common. This is because such active matrix LCDs can produce high quality images at reasonable cost.
Recently, liquid crystal display devices with light, thin, and low power consumption characteristics are used in office automation equipment and video units and the like. Driving methods for such LCDs typically include a twisted nematic (TN) mode and a super twisted nematic (STN) mode. Although TN-LCDs and STN-LCDs have been put to practical use, they have a drawback in that they have a very narrow viewing angle. In order to solve the problem of narrow viewing angle, in-plane switching liquid crystal display (IPS-LCD) devices have been proposed. The IPS-LCD devices typically include a lower substrate where a pixel electrode and a common electrode are disposed, an upper substrate having no electrode, and liquid crystals interposed between the upper and lower substrates.
A detailed explanation about operation modes of a typical IPS-LCD panel will be provided referring to FIGS. 1, 2A and 2B.
As shown in FIG. 1, upper and lower substrates 1 and 2 are spaced apart from each other, and a liquid crystal layer 3 is interposed therebetween. The upper and lower substrates 1 and 2 are called color filter substrate and array substrate, respectively. Pixel and common electrodes 4 and 5 are disposed on the lower substrate 2. The pixel and common electrodes 4 and 5 are parallel with and spaced apart from each other. The pixel and common electrodes 4 and 5 apply an electric field 6 horizontal to the liquid crystal layer 3. The liquid crystal layer 3 has a negative or positive dielectric anisotropy, and thus it is aligned parallel with or perpendicular to the horizontal electric field 6, respectively.
FIGS. 2A and 2B conceptually illustrate operation modes of a conventional IPS-LCD device. When there is no electric field between the pixel and common electrodes 4 and 5, as shown in FIG. 2A, the long axes of the liquid crystal molecules maintain an angle from a line perpendicular to the parallel pixel and common electrodes 4 and 5. Herein, the angle may be 45 degrees, for example.
On the contrary, when there is an electric field between the pixel and common electrodes 4 and 5, as shown FIG. 2B, there is an in-plane horizontal electric field 6 parallel with the surface of the lower substrate 2 between the pixel and common electrodes 4 and 5. The in-plane horizontal electric field 6 is parallel with the surface of the lower substrate 2 because the pixel and common electrodes 4 and 5 are formed on the lower substrate 2. Accordingly, the liquid crystal molecules are twisted so as to align, for example, the long axes thereof with the direction of the horizontal electric field 6, thereby the liquid crystal molecules are aligned such that the long axes thereof are parallel with the line perpendicular to the pixel and common electrodes 4 and 5.
FIG. 3 is a plan view of a lower substrate of the IPS-LCD device according to a related art. Gate lines 21 and a common line 51 are arranged parallel to each other, and data lines 31 are arranged perpendicular to the gate and common lines 21 and 51. A pair of gate and data lines 21 and 31 define a pixel region. At a crossing portion of the gate and data lines 21 and 31, a thin film transistor (TFT) 41 that is connected to the gate and data lines 21 and 31 is disposed. The common line 51 transversely crosses the pixel region, and a plurality of common electrodes 52 are disposed perpendicular to the common line 51 and connected thereto at a center of the pixel region. The plurality of common electrodes 52 are spaced apart from each other with a predetermined interval therebetween.
A plurality of pixel electrodes 62 are disposed parallel to the data line 31 and connected to a pixel connecting line 61, which is disposed above the gate line 21. Since the pixel connecting line 61 overlaps a portion of the gate line 21, the pixel connecting line 61 and the portion of the gate line 21 constitute a storage capacitor 64. Namely, the pixel connecting line 61 acts as a first electrode of the storage capacitor 64, while the portion of the gate line 21 acts as a second electrode of the storage capacitor 64.
Furthermore, one of the pixel electrodes 62 is electrically connected with the TFT 41. The plurality of common electrodes 52 and the pixel electrodes 62 are spaced apart from each other with a predetermined interval therebetween and arranged in an alternating pattern. Therefore, each common electrode 52 is parallel to an adjacent pixel electrode 62.
By the above-described structure and with additional parts such as polarizers and alignment layers, the IPS-LCD device displays images. The IPS-LCD device has wide viewing angles since the pixel and common electrodes are both placed on the lower substrate, as shown in FIG. 3. Namely, the in-plane horizontal electric field generated by the common and pixel electrodes makes it possible to provide the wide viewing angles.
However, in the IPS-LCD device, a color-shift, which depends on the viewing angle, still remains. It is already known that this color-shift is not acceptable for full color-image display. This color-shift is related to a rotational direction of the liquid crystal molecules under application of electric field when the applied voltage is greater than a threshold voltage. Moreover, this color-shift is caused by increasing or decreasing of a retardation (xcex94nxc2x7d) of the liquid crystal layer with viewing angle.
To overcome the problem of color-shift, for example, U.S. Pat. No. 5,745,207 discloses new type IPS-LCD as shown in FIG. 4.
FIG. 4 is a plan view of an exemplary array substrate for the IPS-LCD according to the conventional art. Since the array substrate shown in FIG. 4 is similar to or somewhat the same as the substrate shown in FIG. 3, some explanation is omitted hereinafter.
Compared with the substrate of FIG. 3, although the array substrate of FIG. 4 has similar structure and configuration to that of FIG. 3, the plurality of common and pixel electrodes 52 and 62 have a herringbone shape. The plurality of common electrodes 52 are respectively angled with respect to the common line 51 and connected to each other by the common line 51. The plurality of pixel electrodes 62 are also bent at the central portion of the pixel region that is defined by the pair of the gate and data lines 21 and 31. Therefore, the pixel region is divided into two domains A and B.
From the structure and configuration shown in FIG. 4, liquid crystal molecules 71 and 72, which are positioned in the first domain A and the second domain B, respectively, are twisted in the opposite direction when the voltage is applied to the common and pixel electrodes 52 and 62. Namely, the liquid crystal molecule 71 in the first domain A turns clockwise due to the horizontal electric field generated between the common electrode 52 and the pixel electrode 62, while the liquid crystal molecule 72 in the second domain B turns counterclockwise. In the IPS-LCD of FIG. 4, since the liquid crystal molecules in the domains A and B are symmetrically rotated in opposite directions so as to compensate for the angular dependence of each other, grey level inversion and color shift are eliminated to improve the viewing angle characteristics.
However in the above-mentioned IPS-LCD, the pixel electrodes are formed in a different plane than the common electrodes. In other words, the common electrodes are formed with and in the same plane as the gate line in order to decrease the process steps of manufacture, while the pixel electrodes are formed with and in the same plane as the data line. Therefore, the common electrodes and the pixel electrodes are formed of an opaque metallic material, thereby resulting in the decrease of the aperture ratio.
Accordingly, the present invention is directed to an IPS-LCD device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An advantage of the present invention is to provide an array substrate for use in the IPS-LCD device having an increased aperture ratio.
Another advantage of the present invention is to provide the array substrate for use in the IPS-LCD device, which has a wide viewing angle.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. These and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
In order to achieve the above advantage, the preferred embodiment of the present invention provides an array substrate for use in an in-plane switching liquid crystal display device including: a substrate; a gate line arranged in a first direction on the substrate; a data line arranged in a second direction perpendicular to the gate line, the data line define a pixel region with the gate line; a plurality of common electrodes located in the pixel region and arranged in the second direction; a common line arranged in the first direction and connected to the plurality of common electrodes; a plurality of pixel electrodes located in the pixel region and arranged in the second direction, the plurality of pixel and common electrodes having at least one bent portion and being arranged in an alternating manner with a predetermined interval between adjacent pixel and common electrodes; and a plurality of light-shielding patterns made of the same material as the data line, each light-shielding pattern disposed between one end of the pixel electrode and the intersection of the common line and common electrode.
The above-mentioned array substrate further includes: a thin film transistor that is connected to the gate line and the dat line and includes tha gate electrode, the source electrode and the drain electrode; and a pixel connecting line that extends from the drain electrode and is connected to the plurality of pixel electrode. The pixel connecting line is disposed at the end of the common electrode and overlapped by the common electrode.
Each light-shielding pattern is disposed at an acute angle area where each common electrode forms an acute angle with the common electrode.
In another aspect, the array substrate further includes a capacitor electrode that is made of the same material as the data line and overlapped by the common line to form a storage capacitor, wherein the capacitor electrode is connected to the plurality of light-shielding patterns. One of the plurality of common electrodes extends over the adjacent pixel region. The plurality of common and pixel electrodes has a substantially zigzag shape, and the data line also has a substantially zigzag shape. A portion of the data line is overlapped by a portion of the adjacent common electrode.
In another aspect, an embodiment in accordance with the principles of the present invention provides a method of fabricating an array substrate for in-plane switching liquid crystal display device. The method includes: forming a gate line and a gate electrode on a substrate, wherein the gate electrode is connected ot the gate line, and wherein the gate line is arranged in a first direction; forming a gate insulation layer on the substrate to cover the gate line and the gate electrode; forming an active layer on the gate insulation layer and over the gate electrode; forming an ohmic contact layer on the active layer; forming a data line, a source electrode, a drain electrode, a pixel connecting line and a plurality of light-shielding patterns, thereby defining a intermediate structure, wherein the data line is arranged in a second direction perpendicular to the gate line, wherein the source electrode extends from the data line, and wherein the drain electrode extends from the pixel connecting line; forming a passivation layer over the whole surface of the substrate to cover the said intermediate structure, the passivation layer has a plurality of contact holes; and forming a common electrode and a plurality of common and pixel electrodes, wherein the common electrode is arranged in the first direction, wherein the plurality of common and pixel electrodes are arranged in the second direction and have a substantially zigzag shape, wherein the plurality of common and pixel electrodes are arranged in an alternating manner with a predetermined interval therebetween, and wherein each pixel electrode is connected the pixel connecting line through each contact hole.
Each light-shielding pattern is disposed between one end of the pixel electrode and the intersection of the common line and common electrode.
In another aspect, the method further includes forming a capacitor electrode when forming the data line. The capacitor electrode is overlapped by the common line to form a storage capacitor and connected to the plurality of light-shielding patterns. One of the light-shielding patterns is connected to one of the pixel electrodes through one of the contact holes. The data line has a substantially zigzag shape. A portion of the data line is overlapped by a portion of the adjacent common electrode.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.